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Spatial and Temporal Distribution of Vehicle Exhaust Emission Gradients Near Highways in Somerville, Massachusetts

Ash, C*; Durant, J*; Brugge, D*; Zamore, W; Wood, E; Herndon, S; Jayne, J; Kolb, C; Knighton, W§

doi: 10.1097/01.ede.0000340387.54975.4c
Abstracts: ISEE 20th Annual Conference, Pasadena, California, October 12–16, 2008: Contributed Abstracts

*Tufts University, Medford, MA, USA; †Mystic View Task Force, Somerville, MA, USA; ‡Aerodyne Research, Inc., Billerica, MA, USA; and §Montana State University, Bozeman, MT, USA.

Abstracts published in Epidemiology have been reviewed by the organizations of Epidemiology. Affliate Societies at whose meetings the abstracts have been accepted for presentation. These abstracts have not undergone review by the Editorial Board of Epidemiology.


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Populations living in the vicinity of highways, freeways or major roads may be at risk of adverse health effects, such as reduced lung function, asthma, cardiovascular disease, and lung cancer, due to the elevated levels of automobile exhaust pollutants. To date, relatively little work has been done to characterize air pollution gradients near heavily trafficked roadways. In January 2008, we conducted a study to measure near-highway air pollutant gradients in temperatures < 0°C in the greater Boston area.

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The objectives of the study were to characterize the spatial and temporal distribution of pollutants, to determine the extent of the air pollution gradient, and to look for correlations between individual pollutants in near-highway air.

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Several pollutants were studied, including particle-bound polycyclic aromatic hydrocarbons (PPAH), nitrogen oxides (NOX), carbon oxides (CO2 and CO), aromatic hydrocarbons (benzene, toluene and xylene isomers), size and chemically-speciated particulate mass loadings, and total particle number concentrations (CPC; 7 nm to 2.5 μm). Pollutant concentration, temperature, wind speed and direction data were collected using a mobile air-monitoring laboratory. Continuous measurements of pollutants were repeatedly taken along four transects perpendicular to Interstate 93 in Somerville, Massachusetts, from 6 AM to 11 AM, resulting in data showing air pollution gradients in real-time over the course of the morning.

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Downwind transect results indicate that CO decreased approximately 2-fold (800 to 400 ppb) over a 200-m distance from the highway, CO2 decreased only slightly (425 to 400 ppm), NOX decreased approximately 4-fold (50 to 13 ppb), and CPC decreased approximately 3-fold (90,000 to 30,000 particles/cm3). Upwind transect results indicate that CO decreased approximately 3-fold (2100 to 700 ppb) over a 50 m distance from the highway, CO2 decreased slightly from 430 to 400 ppm, NOX decreased approximately 4-fold (48 to 12 ppb), and CPC decreased approximately 3-fold (60,000 to 20,000 particles/cm3). All pollutant concentrations declined following sunrise, likely due to the break-up of the nocturnal thermal inversion, which reduces vertical mixing of surface emissions. CO, CO2, NOX, and CPC concentrations decreased 4-fold (800 to 400 ppb), slightly from 425 to 400 ppm, 5-fold (50 to 10 ppb), and 4-fold (80,000 to 20,000 particles/cm3), respectively, for both upwind and downwind transects between 7:00 and 10:00 AM. PPAH and aromatic hydrocarbon data were substantially scattered, a result possibly related to emission sources. The number concentration of fine particulate matter was dominated by particles less than 60 nm in diameter. Particle number concentration displayed a more pronounced gradient than the particle mass gradient. The highway enhancement in the mass of particulate matter consisted mainly of organic and sulfate particulate matter.

© 2008 Lippincott Williams & Wilkins, Inc.